1. Field of the Invention
The present invention relates to an ophthalmologic apparatus and, more particularly, to an ophthalmologic apparatus for picking up an image of an eye to be examined, obtaining the position of a bright point formed by a light beam radiated onto the eye to be examined by image processing, and measuring the curvature of a cornea or the eye refracting power.
2. Related Background Art
When the curvature of a cornea or the eye refracting power is measured in an ophthalmologic apparatus, a light beam is radiated onto an eye to be examined, and the position of a bright point (a point illuminated with reflected light) formed by light reflected by the cornea or the fundus of the eye of the radiated light beam must be obtained.
In order to obtain this position, a method of picking up an image of the eye to be examined, and executing image processing is known. At this time, one bright point normally extends over a plurality of pixels.
For this reason, the apparatus comprises a program and an MPU (microprocessor) for obtaining the position of the bright point with high precision, and the program is executed by the MPU. Alternatively, the apparatus may comprise a special-purpose hardware arrangement for realizing this processing.
FIG. 12 is a flow chart showing an example of the program. The operation of this flow chart will be described below.
Pixels for one frame of the eye to be examined are stored in a memory. The memory memorizes luminance data in units of pixels (step S1).
Then, the image of the eye to be examined is divided into a plurality of regions, each of which is expected to include one bright point. The luminance data of all pixels in each region are scanned in units of regions, and are compared with a predetermined threshold to detect pixels exceeding (or equal to or larger than) the threshold. The positions of the detected pixels are memorized (steps S2 to S5).
The centroid of the pixels exceeding (or equal to or larger than) the threshold is calculated for each region, and is determined as the position of the bright point (step S6).
As an example of the special-purpose hardware arrangement, a technique disclosed in Japanese Laid-Open Patent Application No. 63-49131 is known. This special-purpose hardware arrangement stores pixels in an image memory, and at the same time, supplies luminance data and position information of pixels exceeding the threshold to the MPU. The MPU calculates the centroid of pixels exceeding (or equal to or higher than) the threshold for each region, and determines it to be the position of the bright point.
However, in the technique for causing the MPU to execute the program, the luminance data of all pixels must be scanned, and must be compared with a predetermined threshold to detect pixels exceeding (or equal to or higher than) the threshold. For example, in an image defined by 512.times.512 pixels, the total number of pixels is 262,144, and even if a high-speed MPU is used, too much time is required for processing.
In the example comprising the special-purpose hardware arrangement, the arrangement of the apparatus is complicated, resulting in an expensive apparatus.